Several methods and techniques have been developed to introduce steam into a process fluid or slurry to warm, cook or purify the process fluid or slurry. Some examples of the prior art include spargers, mixing tees, venturi-type injection systems and modulating injection systems.
U.S. Pat. No. 2,202,573 to Coppock discloses an early mixing jet cooking device. The Coppock device is comprised of a single orifice steam ejector in which a continuous stream of steam was mixed with a liquid or slurry, generally comprised of an amylaceous material. The Coppock device was comprised of a vertical cylindrical chamber through the top of which a downwardly converging steam nozzle is projected for supplying steam from a pipe controlled by a valve. The steam nozzle extends proximate the mouth of a downwardly divergent delivery nozzle coaxial with the steam nozzle and which projects upwardly inside the chamber from the base and continuing in the form of a delivery pipe. At the point where the steam nozzle and the delivery nozzle met, a flour suspension feed chamber was laterally connected for supplying the flour suspension into the path of steam provided by the steam nozzle. The flour then becomes cooked by the heat of the steam which condenses and the paste collects in a steadying chamber and is finally passed out through an exit pipe.
In addition to U.S. Pat. No. 2,202,573 there exists other devices such as described in U.S. Pat. No. 3,984,504 to Pick and U.S. Pat. No. 4,732,712 to Burnham et al. The Pick device is essentially a variable pressure modulatable Sparger Tube contained within a process flow tube whose construction encompasses a number of moving parts and very small steam orifices. As such, the device is subject to clogging, plugging and steam hammering, particularly when used to heat slurries, and in many cases, when used to heat solutions with dissolved solids concentrations in excess of 1%.
The device described by Burnham is an internally vained mixing tee with a separate steam flow control valve. Thus, it constitutes a variable steam pressure device within the fixed volume mixing tee. While this heater has fewer moving parts than the Pick device, it fails to provide broad rangeability and is subject to steam hammer when its operating parameters exceed narrow limits within each units operational configuration, i.e.--delta T, steam flow, and process fluid flow.
Mixing jet cooking devices, such as those produced by Q-JET.RTM. or the Hydro-Heater.TM. produced by Hydro-Thermal Corporation, continue to utilize separate steam and liquid/slurry inlets, often having attached valves to control the inflow of steam or liquid/slurry, respectively. U.S. Pat. No. 5,743,638 to Cummins/Perry, directed to a "Dual Control Mixing Jet Cooker", describes an actuator connected to the cooking device that provides a steam jet that enters the cooking device. The steam and liquid inlets converge in a "combining" or "mixing" tube, which is an open ended cylinder through which the steam jet shoots. Between the open end of the Venturi and the skirt of the steam jet nozzle is a gap which permits the liquid or slurry to be drawn into the Venturi where it mixes with the jet of steam and condenses, heating the slurry which is expelled out of the mixing tube as a paste.
The single-orifice steam ejector of the prior art has been improved upon by a multi-orifice plate, which is advantageously disposed between the steam source and the mixing tube. The multi-orifice plate comprises a circular disk or plate-like member having a plurality of holes. The holes are arranged to operatively engage with an equivalent number of similarly arranged, conically-tipped pins. The pins are mounted on a valve member which, under the force of an actuating means, move into and out of the holes on the orifice plate in order to regulate the flow of steam from the steam source into the mixing tube, thus forming a multi-jet array. The multi-jet array enables the disbursement of high pressure steam into the process feed from a plurality of equal-pressure small jets, permitting intimate contact of a greater cold process flow surface area with the steam, which results in rapid to instantaneous steam condensation.
While a micro-jet array accomplishes the objective of quick condensation when heating relatively cold feed materials and discharging the heated flow into atmospheric conditions, it encounters acoustical steam hammer difficulties when applied to process flows at elevated process feed temperatures, i.e.--approaching the atmospheric boiling point of the process fluid. This is particularly true when processing materials requiring heated temperatures in excess of the atmospheric boiling temperature of the fluid or medium and/or utilizing a low pressure steam supply (30-70 PSIG), coupled with low temperature differential requirements. The collapse of a steam bubble within a pipe or other vessel and/or the subsequent jarring contact of the condensed gas into the piping or equipment is referred to as "steam hammer". Steam hammer is experienced as a loud noise and the violent vibration of the pipes, vessels or other equipment in the immediate vicinity. The loud noise is undesirable as, by itself or in combination with the noise of other operating machinery in the vicinity, it can cause discomfort or hearing loss to persons in the work environment. The violent vibration of the equipment also causes the disintegration of components in the equipment, increasing maintenance costs and increasing the likelihood of a system failure or of an injury to a person in the work environment.
Therefore, there exists a need for a fluid mixer, such as a direct steam injection heater, which provides a broad range of operation with freedom from acoustical steam hammer.